1. Field of the Invention
The present invention relates to a screw tightening apparatus which screws a bolt into a screw hole of an object to be screwed.
2. Description of the Related Art
Apparatuses have thus far been known that tighten a screw with a screw tightening unit attached to a tip portion of a robot (for example, Japanese Laid-open Patent Publication No. 6-218637). The apparatus according to Japanese Laid-open Patent Publication No. 6-218637 includes a circular disk-shaped magazine having a plurality of screw retaining grooves formed along the outer periphery, and a nut runner which moves relative to the magazine. A bolt is removably and elastically supported in each of the retaining grooves of the magazine, and a socket of the nut runner is fitted on the head of the bolt. Then the magazine is rotated so as to remove the bolt from the magazine, and the bolt is tightened by the nut runner.
However, with the apparatus according to Japanese Laid-open Patent Publication No. 6-218637, the magazine has to be rotated in order to remove the bolt from the magazine, and therefore a complicated mechanism has to be employed. In addition, the bolt has to be completely removed from the magazine before the bolt is tightened by the nut runner, which prolongs the cycle time of the bolt-tightening process as a whole.